2007 Volume 45 Issue 4 Pages 242-255
Relationship between hand positions (HPs) and the corresponding ranges of arm posture (RAPs) was studied computationally for application to rehabilitation using exercise devices which, such as a kind of robot-aided exercise machine, require users to control their HP in 3-dimensional space. A method to calculate the RAP for a HP using a concept of redundant degrees of freedom with a model of upper extremity was shown. The RAPs for 224 HPs sampled from the entire reachable area were obtained by the method. After several RAPs for some example HPs were shown, general characteristics of the joints over all the HPs were investigated using the “allowance ratio” (AR) as an index of controllability of joint. The AR was defined as the ratio of allowable range of a joint for a HP to the full range of the joint. The AR of each joint was calculated for every HP, and the frequent distributions of ARs for all joints were shown. ARs of wrist and forearm (supination/pronation) for most of HPs were over 90%, which suggested these joints might not be controlled. In contrast, ARs of shoulder azimuth and elbow for most of HPs were under 30%. These joints could be controlled better. ARs of both shoulder elevation and rotation were distributed rather widely, but the peaks were in different area; 10-30% for elevation and 80-90% for rotation. These results suggested that at least one degree of freedom of shoulder might be hard to be controlled. Several relationships between HPs and joints were investigated, including those between elbow and shoulder-hand distance, elevation and height of HP, and shoulder azimuth and HP azimuth. Some of the relationships were shown as approximate expressions. The method and results would be useful to design future rehabilitation with the exercise devices.
